docs: add a crude approximation of intersphinx toctrees.

This is a pretty awful hack. We could do this properly after one of
the following issues is fixed:
  * sphinx-doc/sphinx#701
  * sphinx-doc/sphinx#1836

docs/conf.py

@@ -19,6 +19,8 @@ extensions = [
 with open(".gitignore") as f:
     exclude_patterns = [line.strip() for line in f.readlines()]
 
+master_doc = "cover"
+
 intersphinx_mapping = {"python": ("https://docs.python.org/3", None)}
 
 todo_include_todos = True

docs/cover.rst

@@ -0,0 +1,8 @@
+The nMigen documentation
+########################
+
+.. toctree::
+   :maxdepth: 1
+
+   index
+   Board definitions <https://nmigen.info/nmigen-boards/latest/>

docs/index.rst

@@ -1,5 +1,5 @@
-The nMigen core manual
-######################
+Core language
+#############
 
 .. warning::
 
@@ -12,13 +12,3 @@ The nMigen core manual
    install
    start
    lang
-
-Index
-=====
-
-* :ref:`genindex`
-
-Search
-======
-
-* :ref:`search`